arXiv subjects

Chayan Purkait

Publications and source records attributed to Chayan Purkait.

5 recordsLinked to original sources

arXiv2026

Enhanced quantum thermometry near a dissipative phase transition in a driven Kerr cavity

We investigate quantum thermometry in a driven--dissipative Kerr cavity coupled to a thermal reservoir. The system exhibits a finite-size precursor of a dissipative phase transition, characterized by a pronounced minimum of the Liouvillian gap and a sharp jump in the steady-state physical observables such as average photon number at the critical driving strength. We show that this regime leads to strong enhancement of the quantum Fisher information (QFI) for temperature estimation. Using an effective two-branch description, we show that the enhancement originates from temperature-induced redistribution of the weight factors in photon number distribution between low- and high-photon-number branches, which is described by an effective binary Fisher information. By optimizing the coherent drive, the enhanced response persists over an extended low-temperature, low-thermal-occupation regime and yields a favorable relative temperature-uncertainty bound. These results identify finite-size precursors of dissipative phase transitions in Kerr-cavity platforms as useful resources for tunable nonequilibrium quantum thermometry. We further show that the predicted thermometric enhancement is accessible in a parameter regime compatible with circuit quantum electrodynamics (circuit-QED) platforms.

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arXiv2025

Asymptotic freedom in the dephased charging of quantum batteries

Quantum batteries, small-scale energy storage devices based on quantum systems, offer the potential for enhanced charging performance through quantum effects such as coherence and collectivity. In this work, we study the collective charging of quantum batteries consisting of N qubits, coupled to a driven qubit charger in a star configuration, with controlled pure dephasing acting on the charger. We investigate how an "asymptotic freedom"-like behavior, in which all the energy deposited into the battery can be extracted as work, resulting in the ergotropy-to-energy ratio approaching unity, can emerge in the steady state of the battery. We show that the ergotropy-to-energy ratio increases with the number of qubits and approaches unity asymptotically as 1 - O(1/N). In the large-N limit, the emergence of approximate ground-state degeneracy of the collective battery system leads to this asymptotic freedom behavior, despite the battery state remaining mixed. We also discuss the scaling behavior of the charging time of the battery with N.

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arXiv2024

Quasi-probability distribution of work in a measurement-based quantum Otto engine

We study the work statistics of a measurement-based quantum Otto engine, where quantum non-selective measurements are used to fuel the engine, in a coupled spin working system (WS). The WS exhibits quantum coherence in the energy eigenbasis at the beginning of a unitary work extraction stage in presence of inter-spin anisotropic interaction. We demonstrate that the probability of certain values of stochastic work can be negative, rendering itself akin to the quasi-probability distribution found in phase space. This can be attributed to the interference terms facilitated by quantum coherence. Additionally, we establish that coherence can improve the average work in finite time. Subsequently, we compare the work distribution with a standard QOE operating between two heat baths. We find that, because of the absence of quantum coherence, the probability of stochastic work cannot be negative in a standard QOE.

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arXiv2023

Anisotropy-assisted thermodynamic advantage of a local-spin thermal machine

We study quantum Otto thermal machines with a two-spin working system coupled by anisotropic interaction. Depending on the choice of different parameters, the quantum Otto cycle can function as different thermal machines, including a heat engine, refrigerator, accelerator and heater. We aim to investigate how the anisotropy plays a fundamental role in the performance of the quantum Otto engine operating in different time scales. We find that while the efficiency of the engine efficiency increases with the increase in anisotropy for the quasistatic operation, quantum internal friction and incomplete thermalization degrade the performance in a finite time cycle. Further, we study the QOE with one of the spins, the local spin, as the working system. We show that the efficiency of such an engine can surpass the standard quantum Otto limit, along with maximum power, thanks to the anisotropy. This can be attributed to quantum interference effects. We demonstrate that the enhanced performance of a local-spin QOE originates from the same interference effects, as in a measurement-based QOE for their finite time operation.

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arXiv2023

Measurement-based quantum Otto engine with a two-spin system coupled by anisotropic interaction: enhanced efficiency at finite times

We have studied the performance of a measurement-based quantum Otto engine (QOE) in a working system of two spins coupled by Heisenberg anisotropic interaction. A non-selective quantum measurement fuels the engine. We have calculated thermodynamic quantities of the cycle in terms of the transition probabilities between the instantaneous energy eigenstates, and also between the instantaneous energy eigenstates and the basis states of the measurement, when the unitary stages of the cycle operate for a finite time $\tau$. The efficiency attains a large value in the limit of $\tau \rightarrow 0$ and then gradually reaches the adiabatic value in a long time limit $\tau \rightarrow \infty$. For finite values of $\tau$ and for anisotropic interaction, an oscillatory behaviour of the efficiency of the engine is observed. This oscillation can be interpreted in terms of interference between the relevant transition amplitudes in the unitary stages of the engine cycle. Therefore, for a suitable choice of timing of the unitary processes in the short time regime, the engine can have a higher work output and less heat absorption, such that it works more efficiently than a quasi-static engine. In the case of an always-on heat bath, in a very short time the bath has a negligible effect on its performance.

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